The invention relates to grit washers, and more particularly, to a bearing assembly for use in a grit washer.
Wastewater treatment plants typically utilize grit handling equipment which aids in reducing maintenance cost and eliminates grit related operational difficulties. This includes protecting sludge pumps, piping, centrifuges, etc. from the scouring action of grit and preventing grit from reducing the plant""s overall efficiency due to clogged sumps, pipes, channels and digestion tanks.
Grit washers, such as SW type grit washers, are commonly used in wastewater treatment plants to dewater and wash grit, which has been removed from the inlet flow by other collection equipment means, to a low putrescible content of approximately 1.5 percent. When grit is removed in a dry state, water is added to the grit washer to float out all putrescible matter which is then returned to the plant flow. The grit is removed by being conveyed up an inclined steel screw trough by a screw conveyor. Grit washers typically consist of a steel tank (sized to accept the possible flow ranges while providing ample surface area for settling velocities), a screw conveyer, bearing assemblies supporting the ends of the screw conveyor shaft, support structures, a drive unit, inlet pipes, an effluent weir and a discharge trough.
One commercially available grit washer incorporates a steel sleeve and bronze bushed steel pipe sectional screw design which mates with a cast-iron or fabricated steel stub shaft which in turn is machined for lubrication entry. The stub shaft itself is mounted to the bottom of the screw trough hopper, and includes a gasket, grease grooves and drilling and tapping for alemite grease fittings, in order to allow for external greasing and lubrication of the screw bushing and shaft. In order to check for wear, the trough must be fully dewatered, cleaned out and the stub shaft removed for inspection. If the bronze bushing inside the screw pipe end is worn, then the entire screw assembly needs to be disconnected from the drive shaft and fully removed from the tank for a full inspection and replacement of the internal bushing, if required.
Another commercially available grit washer provides a pivoting screw design wherein the screw conveyor can be fully lifted out of the collection tank liquid to facilitate inspection and maintenance of the bottom screw bearing assembly.
The present invention relates to an improved grit washer. The grit washer includes a screw conveyor having one end supported by a bearing assembly. The bearing assembly is positioned outside of the grit washer tank. With the bearing assembly mounted to the exterior of the grit washer tank, the bearing assembly is easily accessible for inspection and maintenance without the need to drain the tank or lift the screw conveyor out of the tank. The bearing assembly itself can more easily be repaired or replaced if necessary. The external placement of the bearing assembly also isolates the bearing assembly from the abrasive grit in the tank thereby minimizing damage to the bearing assembly caused by the grit.
The bearing assembly preferably includes a bearing housing, a wear plate, a gland, an end plate and various seals. In one embodiment, the wear plate and gland are fabricated from non-metallic materials to eliminate the need for a lubrication system. Both the gland and the wear plate support the drive shaft thereby sharing the load and increasing their useable lives. When mounted to the exterior of the grit washer tank, the gland is easily accessible without the detachment of the remainder of the bearing assembly from the tank. Further, the orientation of the wear plate and gland within the bearing housing can be changed to extend the lives of those components.
Features and advantages of the invention will become apparent to those of ordinary skill in the art upon review of the following detailed description, claims, and drawings.